Differences between
analog signal and digital signal are given below :
·
Analog signal is a continuous signal
whereas Digital signal is discrete time signal.
·
Analog signal is denoted by sin
waves whereas Digital signal is denoted by square waves.
·
Analog signal has high noise whereas
Digital signal has less noise.
·
Analog signal is stored in the form
of wave signal whereas Digital signal is stored in the form of binary bit.
·
Analog signal has less cost whereas
Digital signal has high cost.
·
Analog signal example is - Human
voice whereas Digital signal example is Computer system.
Purely digital signals exist as a sequence of
samples. These samples might be stored somewhere or digitally processed. They
are both discrete in time and quantized in amplitude.
Analog signals are the physical signals that propagate
through some medium i.e. a circuit, cable, the air, etc. They are continuous in
both time and amplitude.
The reason I started by talking about “purely” digital
signals is because that’s really an abstraction. The reality is that everything
in this world is analog. When we talk about a digital circuit which
reads/writes a byte of data, the reality is that the circuit operates on analog
inputs and outputs. But by intelligently designing the circuit we can abstract
away these details and just think about the digital signals. A wireless
transmission that contains digital information still ultimately uses an analog
signal to propagate through the air.
Analog signal:
(continues signals )
1.analog signal is continues signals
which represents physical measurements .
2.wave : denoted by sine wave
3. Example : Human voice in air,
analog electronic devices.
4.Representation:Uses continuous
range of values to represent information
5.Data transmissions :Subjected to
deterioration by noise during transmission and write/read cycle.
6. Uses : Can be used in analog
devices only. Best suited for audio and video transmission.
Digital Signals
1.Digital signals are discrete time
signals generated by digital modulation.
2.wave : denoted by square wave
3.Examples :Computers, CDs, DVDs,
and other digital electronic devices.
4. Representation: Uses discrete or
discontinuous values to represent information
5.Data Transmission: Can be
noise-immune without deterioration during transmission and write/read cycle.
6.Uses :Best suited for Computing
and digital electronic.
The following graph is more clear in
understanding there signals..
Main difference you get between analog and
digital signals is that analog real time Signals and digital signals that are
performed within the system it's basically your voice my voice and everyone
else's voice is analogue because suppose you are speaking a sentence you are
going to spell it till the end Undertaker instead of time I can measure a
certain DB of noise coming from your mouth so this noise is introduced into the
transducer which converts it into voltage signals now the signals are analog in
nature the main thing which we get defect is analogue parts has many losses and
also the computational time is pretty high compared to the digital so we use an
analogto digital converter to convert these analog signals into digital signals
by the help of sampling that is we take the values of the signal at every small
instant of time this small instant of time is very small and it has to follow
nyquist criterion I am not going into the details of this criterion about it in
the later stages but the sampling is basically we are taking the values of this
signal at every small instant of time such that will get a large value of the
data of the original signal. These data are converted into zeros and ones and
processes in the system which are digital in nature and finally after all the
computations it is converted do analog
To understand this
difference, let us go back a bit and start with the very basics:
Q: What is a signal?
- A signal is a plot of the value of
a physical quantity/parameter with respect to time. In other words, a signal
carries information about the change in the value of a quantity/parameter over
a period of time. The physical quantity could be anything that we are trying to
measure, like temperature, speech, light intensity etc.
NOTE- If the physical quantity being
measured is an electrical parameter, like Voltage or Current, then the signal
is called an electrical signal.
- An analog signal is continuous
with respect to time; meaning its value changes continuously with time. In
other words, an analog signal will have a value at any given instant of time.
For example, the value of an analog signal can be extracted at 0s, 1.5s,
4.908675s etc.
- All real world signals are analog
in nature.
Q: What are signals
used for?
- There are three things that can be
done with a signal:
1.Store the signal for later use
2.Process the signal (convert it to
some other form, perform some operations on the signal etc)
3.Transmit the signal to some other
destination to be used there.
- Now, since analog signals are
continuous, it will have infinite number of values considering the value at
each instant of time. Therefore, storing such a signal requires large amount of
memory; processing requires large processing power or more time; transmitting
requires a large bandwidth.
Q: So, is there an
easy way to handle signals?
- YES. Instead of
measuring/considering the signal value at every instant of time, lets take the
signal value only at desired instances of time. In other words, we consider
signal "samples" at specific instances of time.
- Above picture shows an analog
signal sampled at specific time instances (t1 - t10). Such a signal is called
as a "discrete time signal", since the signal values are represented
at discrete time units. In technical terms, the signal values are called as
"samples" and this process is called as "sampling". Closer these
samples are, more accurate will be the signal representation. The number of
samples to be considered is determined by the "sampling rate" of the
system.
- With discrete time signal, there's
a problem. The amplitude of the samples can be real numbers (5.38239, 13.57236
etc) representing which may become tedious. To overcome this, just like we
divided the x-axis at discrete intervals, let us also divide the y-axis at
discrete intervals.
- If the signal amplitude falls
between 0 and L1, let us round it off to 0. If the signal amplitude falls
between L1 and L2, we round it off to L1 and so on. Again, the closer these
levels are, more accurate will be the signal representation.
- This process is called as "quantization" and the
resulting quantized signal is called a "Digital Signal".
- Most digital systems today make
use of only two signal levels, Level0 and Level1.
- These signal levels have different
names in the world of digital electronics;
Level0 or Logic0/OFF/False/Absent
Level1 or Logic1/ON/True/Present
- That is, at any given instant of
time the signal is either present or it is absent. If it is present, we call it
Logic1, or simply 1, and if it is absent we call it Logic0, or simply 0.
- Analog signals are converted into
digital signals, processed in digital form and converted back to analog on need
basis, because it is easier to handle/work with digital signals.
- we cannot completely do away with
analog signals, so at the earliest possible time we take the analog signal and
if the signal is very weak, we amplify it to a desirable level and convert it
into a digital signal.
Let me try to answer your question
in most easiest way. In text book B.P. Lathi of analog and digital communication system, signals
are defined of four types based on which axis (time or amplitude) is sampled:
1. Continuous time and
continuous amplitude signal: this type of signal is continuous in both axis and
neither of the axis is sampled. These type of signals are also called analog
signal.
2. Continuous time and
discrete amplitude signal: As name suggests, these signals are continuous in
time but discrete in amplitude i.e. signal is sampled in amplitude only.
3. Discrete time and
continuous amplitude signal: These signals are sampled only on time axis and
amplitude is continuous. These signals are also most commonly called just
discrete signals.
4. Discrete time and
discrete amplitude signal: These signals are sampled in both axises i.e. both
time and amplitude axises are sampled. These signals are also called digital
signals.
If you have understood all above 4 definitions, then by now you can understand the difference between analog and digital signal. In analog signal both the axises are continuous whereas in digital signals, both the axises are sampled or discrete.
Analog signal is a continuous signal with
infinite time and magnitude resolution. Real world signals are analog signals,
sound, light, radio waves, etc. Take that real world signal and digitize it
with discrete time steps and finite magnitude resolution, you get digital
signals. Sound file and digital pictures are examples of digital signal.
The key concept for converting between digital and analog
signals is the sampling theorem. In simple terms, a signal
digitized at twice the highest frequency content of an analog signal can be
perfectly reconverted back to analog. For example, we deem 8kHz sampling rate
is good enough to cover the highest pitch female voice, whereas 44kHz was
acceptable for CD recording of a piece of music. However, there are always some
outliers who can or claim they can hear well about 22kHz tones.
Digital audio is technology that can be used
to record, store, generate, manipulate, and reproduce sound using audio signals
that have been encoded in digital form. Following significant advances in
digital audio technology during the 1970s, it gradually replaced analog audio
technology in many areas of sound production, sound recording (tape systems
were replaced with digital recording systems), sound engineering and
telecommunications in the 1990s and 2000s.
A microphone converts sound to an analog
electrical signal, then an analog-to-digital converter (ADC)—typically using
pulse-code modulation—converts the analog signal into a digital signal. This
digital signal can then be recorded, edited and modified using digital audio
tools. When the sound engineer wishes to listen to the recording on headphones
or loudspeakers (or when a consumer wishes to listen to a digital sound file of
a song), a digital-to-analog converter performs the reverse process, converting
a digital signal back into an analog signal, which analog circuits amplify and
send to a loudspeaker.
Digital audio systems may include
compression, storage, processing and transmission components. Conversion to a
digital format allows convenient manipulation, storage, transmission and
retrieval of an audio signal. Unlike analog audio, in which making copies of a
recording leads to degradation of the signal quality, when using digital audio,
an infinite number of copies can be made without any degradation of signal
quality.
Overview
Digital audio technologies in the 2010s are
used in the recording, manipulation, mass-production, and distribution of
sound, including recordings of songs, instrumental pieces, podcasts, sound
effects, and other sounds. Modern online music distribution depends on digital
recording and data compression. The availability of music as data files, rather
than as physical objects, has significantly reduced the costs of distribution.
Before digital audio, the music industry
distributed and sold music by selling physical copies in the form of records
and cassette tapes. With digital audio and online distribution systems such as
iTunes, companies sell digital sound files to consumers, which the consumer
receives over the Internet. This digital audio/Internet distribution model is
much less expensive than producing physical copies of recordings, packaging
them and shipping them to stores.
An analog audio system captures sounds, and
converts their physical waveforms into electrical representations of those
waveforms by use of a transducer, such as a microphone. The sounds are then
stored, as on tape, or transmitted. The process is reversed for playback: the
audio signal is amplified and then converted back into physical waveforms via a
loudspeaker. Analog audio retains its fundamental wave-like characteristics
throughout its storage, transformation, duplication, and amplification.
Analog audio signals are susceptible to noise
and distortion, due to the innate characteristics of electronic circuits and
associated devices. Disturbances in a digital system do not result in error
unless the disturbance is so large as to result in a symbol being
misinterpreted as another symbol or disturb the sequence of symbols. It is
therefore generally possible to have an entirely error-free digital audio
system in which no noise or distortion is introduced between conversion to
digital format, and conversion back to analog.
A digital audio signal may be encoded for
correction of any errors that might occur in the storage or transmission of the
signal, but this is not strictly part of the digital audio process. This
technique, known as "channel coding", is essential for broadcast or
recorded digital systems to maintain bit accuracy. The discrete time and level
of the binary signal allow a decoder to recreate the analog signal upon replay.
Eight to Fourteen Bit Modulation is a channel code used in the audio Compact
Disc (CD).
Conversion process
The lifecycle of sound as it happens usually
is from its source, through an ADC, digital processing, a DAC, and finally as
sound again.
A digital audio system starts with an ADC
that converts an analog signal to a digital signal.
The ADC runs at a specified sampling rate and
converts at a known bit resolution. CD audio, for example, has a sampling rate
of 44.1 kHz (44,100 samples per second), and has 16-bit resolution for each
stereo channel. Analog signals that have not already been bandlimited must be
passed through an anti-aliasing filter before conversion, to prevent the
distortion that is caused by audio signals with frequencies higher than the
Nyquist frequency, which is half of the system's sampling rate.
A digital audio signal may be stored or
transmitted. Digital audio can be stored on a CD, a digital audio player, a
hard drive, a USB flash drive, or any other digital data storage device. The
digital signal may then be altered through digital signal processing, where it
may be filtered or have effects applied. Audio data compression techniques,
such as MP3, Advanced Audio Coding, Ogg Vorbis, or FLAC, are commonly employed
to reduce the file size. Digital audio can be streamed to other devices.
For playback, digital audio must be converted
back to an analog signal with a DAC. DACs run at a specific sampling rate and
bit resolution, but may use oversampling, upsampling or downsampling to convert
signals that have been encoded with a different sampling
What is the difference between analogue and
digital transmission?
When we talk about analogue or digital, we are referring
to the type of transmission of a signal. There are a number of key differences
between analogue and digital signal transmission.
Analogue Transmission
An analogue signal (otherwise known as a wave form) is
characterised by being continuously variable along both amplitude and
frequency. In the case of telephony, when we speak into a handset, our voice is
converted into current, or voltage fluctuations. Those fluctuations in current
are an analogue transmission of the actual voice pattern.
To transmit an analogue signal effectively, we need to
define the frequency in which is operates. In telephony, the usable voice
frequency band ranges from approximately 300 Hz to 3400 Hz, and so the network
provider (phone company) will allocate a bandwidth of around 4,000Hz for voice
transmission.
Because of the limited bandwidth analogue facilities
have, they cannot support high-speed data transmission.
Digital Transmission
Digital signals are much simpler than analogue signals.
Instead of a continuous wave form, analogue signals are made up of a series of
pulses that represent either one bit or zero bits. Each computer system uses a
coding scheme which defines what combinations of ones and zeros make up all the
characters in the character set.
The data (ones and zeros) are carried throughout the
network depending on whether it is an electrical or optical transmission
system.
Electrical
Transmitting digital signals over an electrical system
essentially means that the ones are represented by high voltage and zero bits
are represented as low voltage (or nothing at all).
Optical
In optical networks, the ones are represented as the
presence of light and zeros as the absence of light.
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